The present invention relates to an absorbent article.
Absorbent articles have been known for a long time as sanitary articles. They are used, for example, as diapers, incontinence pads or sanitary napkins. Such absorbent articles are capable of absorbing and retaining liquid body exudates, such as urine, menstrual fluid or blood. Sanitary napkins, for example, are used to absorb fluids discharged before, during and after menstruation. Sanitary napkin s are worn on the outside of the body (externally) and thus differ in so far from tampons which are inserted into the female vagina and can thus be referred to as xe2x80x9cinternalxe2x80x9d products.
The use of known absorbent articles is frequently disadvantageous in so far as the bodyside surface, after liquids have been discharged thereon, comprises wet areas which causes discomfort to the wearer. Tests showed that conventional sanitary napkins rewet if only about 5% of the theoretical liquid absorption capacity of the sanitary napkin has been utilized. Moreover, the discharged body fluids often leave visible residues on the surface of the absorbent article. This causes the user of the article to change the absorbent article more often than it would be necessary as far as the absorbency for liquids is concerned.
It is an object of the present invention to provide an absorbent article, wherein the absorbency of the liquid storage material of the absorbent article is optimally utilized so that as few traces of use as possible are visible on the bodyside surface of the absorbent article, even after prolonged use.
The absorbent article of the invention has the following structure. A liquid-impermeable layer is provided on the side which is away from the wearer""s body when said absorbent article is in use. A primary storage layer is provided above said liquid-impermeable layer. A secondary storage layer is provided above said primary storage layer. A compensation layer is provided above said secondary storage layer, and a cover layer is provided above said compensation layer, said cover layer comprising a central opening. The cover layer comprises a mixture of pulp and polymerized alkene, wherein said mixture comprises at least 50% by weight polymerized alkene. Finally, the absorbent article of the invention includes a liquid-permeable top layer which is disposed toward the wearer""s body when the absorbent article is in use.
It was found to be particularly suitable for the secondary storage layer to include at least one densified section. Preferably, the at least one densified section extends in longitudinal direction of said article. The at least one densified section should be disposed within the projection of said central opening of said cover layer on said secondary storage layer. Particularly suitable results have been achieved with a secondary storage layer which includes at least five densified sections.
Pulp, for example, is suitable as a material for the secondary storage layer. Local densifications in the secondary storage are obtainable, for example, by embossing grooves into the storage. The storage material positioned below the embossed grooves is thereby densified, while the grooves contribute to a targeted liquid transfer on the storage layer and the absorbent article, respectively.
The cover layer, which includes the central opening, is made of a mixture of pulp and polymerized alkene. The mixture preferably includes at least 50 wt. % of polymerized alkene. Excellent results have been achieved with a polymerized alkene content of from 50 to 80 wt. %, in particular 60 wt. %. The cover layer may also be constructed of two layers such that a first layer of a mixture of pulp and polymerized alkene is applied on a second carrier layer of polymerized alkene. The first layer of pulp and polymerized alkene communicates with said liquid-permeable layer disposed toward the wearer""s body when said absorbent article is in use, and said second carrier layer communicates with said compensation layer. Preferred polymerized alkenes are polyethylene, polypropylene and mixtures of polyethylene and polypropylene. Moreover, the cover layer may contain a pigment such as titanium oxide.
It is favorable for the material of the compensation layer to be made from a nonwoven material. The nonwoven material may contain polymerized alkene and/or bicomponent fibers. Furthermore, the surface of the compensation layer which is disposed toward the storage layer may be coated with a surface-active substance which may contain, for example, silicone. The primary storage layer, for example, may consist of an UCTAD material, tissue fluff or a polymer alkene. It is advantageous for the primary storage layer to be constructed such that the peripheral sections thereof are folded inwardly and overlap each other.
Both the liquid-impermeable layer and the liquid-permeable layer may be made using by a polymerized alkene, such as, for example, polyethylene, polypropylene or a mixture thereof. In order to fasten the absorbent article to a garment, the liquid-impermeable layer preferably includes at least one adhesive element and/or adhesive layer. Moreover, the absorbent article of the invention may include laterally disposed flaps. The absorbent article of the invention is preferably used as sanitary product, in particular as sanitary napkin or feminine care liner.
A preferred UCTAD (uncreped through air-dried) material may also be used as primary storage layer. The material includes at least 10 wt. % of high yield pulp fibers, based on its dry weight. A wet strength agent is added in an amount which causes the ratio of wet tenacity to dry tenacity to be at least about 0.1. High yield pulp fibers contain a high amount of lignin which facilitates the wet elasticity of the fibers. The resin bonds formed by the wet strength agent immobilize the wet elastic fibers in a sheetlike structure, which adapts to the structure of the belt on which through drying is effected. During the drying step, the bonds formed by the wet strength agent are cured so that wet-resistant bonds may form which, in turn, impart highly elastic properties to a corresponding web in a wet state. The web maintains this property because, in an UCTAD process, no creping step or other steps are performed which would destroy the bonds again. The UCTAD material is highly suitable to transfer and store liquids because the material is stabilized also in a wet state. Various advantages of the absorbent article of the invention shall now be explained in further detail.
The liquid-permeable top layer which is disposed toward the wearer""s body may, for example, be made of a spun-bonded polypropylene. If suitable pigments, such as titanium oxide, are added to this liquid-permeable top cover layer, this layer prevents to a certain extent the liquid stored in the absorbent article from showing through. This bodyside top layer may also be a nonwoven or film material including a centrally disposed opening.
The next layer is the cover layer, which includes a central opening to facilitate penetration of discharged liquids into the layers further below. This opening may, for example, be punched out and exhibit an oval or dog-bone shape. The cover layer, too, may include pigments, which in turn prevents discharged and absorbed liquids from showing through on the surface of the absorbent article. The cover layer further serves to prevent liquid which has penetrated into the absorbent article from flowing back to the surface, so that no re-wetting occurs and the wearer""s body is kept dry.
This is achieved with a cover layer which is constituted of a coform material. A suitable coform material is, for example, a polypropylene/pulp mixture with a polypropylene content of more than 50 wt. %. Polypropylene contents of 50 to 80 wt. %, in particular, 60 wt. %, were found to be particularly suitable. A coformr material is prepared using pulp that is defiberized and melt-blown polypropylene is prepared. The defiberized pulp and the polypropylene fibers are then mixed and laid on a moving belt, to obtain the desired polypropylene/pulp mixtures. Due to the structure of the coform material, i.e., due to its pulp content, this cover layer absorbs liquid discharged from above and transfers it downward. This is important, for example, when a sanitary napkin is improperly positioned and the liquid does not pass via the punched out opening directly through the foil into the sanitary napkin. The polypropylene, which accounts form more than 50% of the coform material, prevents liquid which has already penetrated into the sanitary napkin from being taken up by the cover layer from below. Accordingly, the coform material results in a considerable improvement of the rewetting properties of the absorbent article. If a corresponding pigmentation is added, absorbed liquid is prevented from showing through, and a so-called stain-hiding effect is achieved.
The rewetting properties of the absorbent article of the invention can further be improved if the cover layer is of a two-layered or three-layered construction. The upper bodyside layer may be the above-described coform material which is a mixture of polypropylene and pulp. This coform material is then preferably applied on a further layer of polymerized alkene, such as polypropylene. Three-layered structures having a coform layer sandwiched between two layers of polymerized alkene are also possible. The polypropylene may be prepared by means of spunbonding processes which result into a nonwoven-type structure. The hydrophobic properties of the polymer alkene effectively prevents liquid, once it has been absorbed in the absorbent body, from flowing back again to the surface of the absorbent article.
The compensation or surge layer is preferably made of a nonwoven material. The nonwoven can be made of polyethylene, polypropylene or other polymerized alkenes, and it can comprise bicomponent fibers. If the absorbent article is a diaper, this compensation layer both serves to store and to transfer the absorbed urine. However, if the absorbent article is a sanitary napkin, the compensation layer has no storage function. In sanitary napkins the compensation layer primarily serves again to keep absorbed liquid invisible.
Apart from nonwoven materials, carded webs can also be used for the compensation layer. Preferred compensation layers have been treated with a surface-active substance. Particularly suitable surface-active agents contain silicone. The surface active agents are applied on the underside of the compensation layer, i.e., on the side which rests on the absorbent body which provides secondary storage. The resulting capillary effects effectively prevent rewetting through the compensation layer.
The absorbent body has a particular function in the absorbent article. It serves to store and distribute liquid which has penetrated into the absorbent article. The liquid-distribution function of the absorbent body can be promoted by a special embossing, which locally increases the density of the absorbent body in longitudinal direction of the absorbent article. The densification can, for example, be effected by embossing lines or grooves. The embossing should at least be in that area which is positioned below the central opening of the cover layer. The embossing may, however, be further extended to the end portions of the absorbent body.
A preferred absorbent body comprises five densified portions extending in longitudinal direction. The embossings reduce the absorbent capacity of the absorbent body in the embossed portions. The penetrated liquid is distributed in the thus formed recesses and is transferred into the primary storage layer below. Moreover, due to the embossing, the thickness of the absorbent body is reduced in its central area, so that the thickness of the absorbent article is larger at the edges than in the central portion. This depression in the central portion increases the wear comport, for example, of a sanitary napkin. If liquid is then discharged on the absorbent body, due to the depression in the central portion, the sanitary napkin has less body contact with the wearer""s skin which increases the feeling of dryness on the body surface. Pulp is a particularly suitable material for the absorbent body and the secondary storage, respectively.
The primary storage layer is positioned directly on the liquid-impermeable layer which serves as a garment-protecting foil. It is preferably made of an UCTAD material, tissue fluff or a melt-blown polypropylene. Apart from storing liquid, the primary storage layer serves to transfer penetrated liquid into the end portions of the absorbent body. The distribution into the end portions can even be promoted in that the primary layer is narrower in the central portion of the absorbent article than in the end portion. If the primary storage is made, for example, of tissue fluff, it is capable of absorbing up to about 2 ml of liquid. Tests have shown that no more than 2 ml of liquid are applied to more than half of all sanitary napkins before they are exchanged. This means that in the major part of used sanitary napkins the entire amount of absorbed liquid is taken up in the layer which is furthest remote from the wearer""s body and contiguous to the garment-protecting foil. As a result, rewetting is optimally prevented and the absorbent liquid will not show through on the bodyside surface of the sanitary napkin. Should more than 2 ml be discharged, the primary storage layer releases any excess liquid upwardly into the secondary storage layer, resulting into the so-called xe2x80x9cbottom-up-filling effectxe2x80x9d, but not until more than 2 ml of liquid have been discharged.
The primary storage layer may also be in the form of a corrugated or pleated web, the corrugation promoting the distributing function of the layer. The corrugations of the web are so arranged that the liquid is transferred in longitudinal direction to the ends of the article. The corrugations extend in cross-direction of the absorbent article such that they form transfer channels in longitudinal direction.